The present invention is directed to hermetically sealed packages that are suitable to protect thin film devices, particularly those sensitive to the ambient environment. Some examples of such devices are organic emitting light diode (OLED) displays, sensors, and other optical devices. By way of example, the present invention will be discussed in the context of OLED displays, but is not limited to such.
OLEDs have been the subject of a considerable amount of research in recent years because of their use and potential use in a wide variety of electroluminescent devices. For instance, a single OLED can be used in a discrete light emitting device or an array of OLEDs can be used in lighting applications or flat-panel display applications (e.g., OLED displays). Traditional OLED displays are known to be very bright, to have a good color contrast, to produce true color, and to exhibit a wide viewing angle. However, traditional OLED displays, and in particular the electrodes and organic layers located therein, are susceptible to degradation resulting from interaction with oxygen and moisture leaking into the OLED display from the ambient environment. It is well known that the life of the OLED display can be significantly increased if the electrodes and organic layers within the OLED display are hermetically sealed from the ambient environment.
Unfortunately, it has been very difficult to develop a sealing process to hermetically seal the OLED display. Some of the factors that make it difficult to properly seal the OLED display include:                (i) that the hermetic seal should provide a barrier for oxygen (10−3 cc/m2/day) and water (10−6 g/m2/day);        (ii) that the size of the hermetic seal should be minimal (e.g., <2 mm) so it does not have an adverse effect on size of the OLED display;        (iii) that the temperature generated during the sealing process should not damage the materials (e.g., electrodes and organic layers) within the OLED display (e.g., the first pixels of OLEDs which are located about 1-2 mm from the seal in the OLED display should not be heated to more than 100° C. during the sealing process);        (iv) that the gases released during sealing process should not contaminate the materials within the OLED display; and        (v) that the hermetic seal should enable electrical connections (e.g., thin-film chromium) to enter the OLED display.        
Of the above challenges, one of the most difficult is the hermetic sealing due to the strong reactivity of organic molecules with oxygen and moisture.
Among the conventional techniques for sealing the OLED display is to use different types of epoxies, inorganic materials and/or organic materials that form the seal after they are cured by ultra-violet light. Vitex Systems manufactures and sells a coating under the brand name of Batrix™, which is a composite based approach where alternate layers of inorganic materials and organic materials can be used to seal the OLED display. Although these types of seals usually provide good mechanical strength, they can be very expensive and there are many instances in which they have failed to prevent the diffusion of oxygen and moisture into the OLED display. Another conventional technique for sealing the OLED display is to utilize metal welding or soldering; however, the resulting seal is not durable in a wide range of temperatures because of substantial differences between the coefficients of thermal expansions (CTEs) of the glass plates and metal in the OLED display.
Another technique for sealing a glass package (such as an OLED display) is disclosed in U.S. Pat. No. 6,998,776, assigned to Corning Incorporated, the entire disclosure of which is hereby incorporated by reference. The technique involves a laser frit sealing technology, which compared to the conventional epoxy sealing method, demonstrates many advantages, such as much higher hermeticity, a high display density with a fixed size of substrate, and application to top emission devices. However, the use of a high power laser to melt the frit materials may lead to one or more disadvantageous results. Indeed, it is possible that the thermal cycle caused by the heating process can cause thermal damage in OLED devices.
In the laser frit sealing technique, the frit is bonded to various device materials such as cathode metal-leads, indium tin oxide (ITO) and other protective materials. Each material on the device side has different thermal properties (e.g., CTE, heat capacity and thermal conductivity). The various thermal properties on the device side can cause a significant variation of the bonding strength between the frit and the device boundary after completing the laser sealing process. In addition, the cathode metal-leads can be delaminated after laser frit sealing. Since the cathode usually consists of multiple layers of two or three different metal elements, each with potentially different CTEs, the relatively fast process of heating and cooling employed in laser frit sealing can occasionally cause damage on the metal cathodes, such as “winkle” effects. The high thermal conductivity of metal leads is also a possible origin of lowering the bonding strength. This is due to the relatively fast heat dissipation during the process of heating the frit with a high power laser.
Accordingly, there are needs in the art to address the aforementioned problems and other shortcomings associated with known techniques of sealing glass packages, such as OLED displays.